Fix #19809 -- Don't check if docs exist in DB.

The docs database is built from the JSON version of the docs, which
doesn't include special pages such as indexes.

This reverts commit 1af4480ae19db8c39b07c28df32a12df72a38f0a.

d51819ecaab91f2d5b91cdc5d01c22b5aeb3f231 has a better and sufficient
fix.

Refs #18930.